Flexible cellular foams such as open-cell polyurethane flexible foams, closed-cell polyurethane flexible foams, latex foams and melamine foams typically have low thermal conductivities in the range of about 0.035 to about 0.060 W/(m K). Materials with low thermal conductivities typically function as insulators, such as rigid polyurethane foam insulation board or expanded polystyrene insulation board.
Heat transfer consists of a combination of the phenomena of conduction, convection and radiation. In a cushion or mattress, heat transfer by radiation is not very large. Instead, heat transfer by conduction and convection are the primary paths for moving heat in and through a cushion or mattress. As a person sleeps on a mattress, the compressed foam underneath the body has reduced air flow paths, and the primary mode of heat transfer in the region below the body is conduction.
Heat is conducted from the body, through the compressed foam and dispersed into cushion or mattress regions where the foam is not compressed as much, which allows natural convection to occur more readily to remove heat from the mattress. Due to the low thermal conductivity of foam, this process is slow and requires a large temperature gradient to drive the conduction of heat at a rate similar to the heat production in a person's body. This results in a large region of hot foam around the body which makes the foam uncomfortable.
U.S. Pat. No. 3,255,128 discloses polyurethane foam compositions containing small particles of metallic aluminum and methods for treating the aluminum particles with phosphoric acid to enhance their usefulness in polyurethane foam. The phosphate aluminum flake was added to insulating polyurethane foam panels to decrease the heat flow through the panels by reducing absorption of heat and radiation.
U.S. Pat. No. 3,833,951 discloses flameproofed mattresses, pillows and sleeping bags. A metallized heat conductive layer is made by mixing a metal with an aqueous vinyl binder, and the frothed mixture is spread on a polyurethane foam having foam thickness between 0.1 to 1.0 inches and dried around 280° C. The final dried coating is 0.5 to 6 mils in thickness.
U.S. Pat. No. 6,772,825 B2 discloses a support surface for patient comfort and to maintain a cool skin temperature by having a refrigerant bladder with boiling point between 23 and 35 degrees Celsius contained within a bladder, a flexible spacer in the bladder such as polyurethane foam, and thermally-conductive aluminum or copper metal strips and a top metal layer located on the outside of the bladder. The strips of metal are used to transfer heat away from refrigerant gas into the surrounding environment. Metallic material was not added to the polyurethane foam reactants prior to producing the foam substrate.
It is useful and desirable to develop improved heat transfer in a cushion or mattress to provide a cooler and more comfortable sleep.